TY  - JOUR
A1  - Assagra, Yuri A.O.
A1  - Altafim, Ruy Alberto Pisani
A1  - do Carmo, Joao P.
A1  - Altafim, Ruy A.C.
A1  - Rychkov, Dmitry
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - A new route to piezo-polymer transducers: 3D printing of polypropylene ferroelectrets
JF  - IEEE transactions on dielectrics and electrical insulation
N2  - Here, a promising approach for producing piezo-polymer transducers in a one-step process is presented. Using 3D-printing technology and polypropylene (PP) filaments, we are able to print a two-layered film structure with regular cavities of precisely controlled size and shape. It is found that the 3D-printed samples exhibit piezoelectric coefficients up to 200 pC/N, similar to those of other PP ferroelectrets, and their temporal and thermal behavior is in good agreement with those known of PP ferroelectrets. The piezoelectric response strongly decreases for applied pressures above 20 kPa, as the pressure in the air-filled cavities strongly influences the overall elastic modulus of ferroelectrets.
KW  - 3D printing
KW  - polymer ferroelectrets
KW  - sensors and actuators
KW  - piezoelectrets
KW  - electret polymers
KW  - soft electro-active materials
KW  - functional materials
KW  - soft matter
Y1  - 2020
U6  - https://doi.org/10.1109/TDEI.2020.008461
SN  - 1070-9878
SN  - 1558-4135
VL  - 27
IS  - 5
SP  - 1668
EP  - 1674
PB  - Inst. of Electr. and Electronics Engineers
CY  - Piscataway
ER  - 
TY  - GEN
A1  - Loupos, Konstantinos
A1  - Damigos, Yannis
A1  - Tsertou, Athanasisa
A1  - Amditis, Angelos
A1  - Lenas, Sotiris-Angelos
A1  - Chatziandreoglou, Chistos
A1  - Malliou, Christina
A1  - Tsaoussidis, Vassilis
A1  - Gerhard, Reimund
A1  - Rychkov, Dmitry
A1  - Wirges, Werner
A1  - Frankenstein, Bernd
A1  - Camarinopoulos, Stephanos
A1  - Kalidromitis, Vassilis
A1  - Sanna, C.
A1  - Maier, Stephanos
A1  - Gordt, A.
A1  - Panetsos, P.
T1  - Innovative soft-material sensor, wireless network and assessment software for bridge life-cycle assessment
T2  - Life-cycle analysis and assessmanet in civil engineering : towards an integrated vision
N2  - Nowadays, structural health monitoring of critical infrastructures is considered as of primal importance especially for managing transport infrastructure however most current SHM methodologies are based on point-sensors that show various limitations relating to their spatial positioning capabilities, cost of development and measurement range. This publication describes the progress in the SENSKIN EC co-funded research project that is developing a dielectric-elastomer sensor, formed from a large highly extensible capacitance sensing membrane and is supported by an advanced micro-electronic circuitry, for monitoring transport infrastructure bridges. The sensor under development provides spatial measurements of strain in excess of 10%, while the sensing system is being designed to be easy to install, require low power in operation concepts, require simple signal processing, and have the ability to self-monitor and report. An appropriate wireless sensor network is also being designed and developed supported by local gateways for the required data collection and exploitation. SENSKIN also develops a Decision-Support-System (DSS) for proactive condition-based structural interventions under normal operating conditions and reactive emergency intervention following an extreme event. The latter is supported by a life-cycle-costing (LCC) and life-cycle-assessment (LCA) module responsible for the total internal and external costs for the identified bridge rehabilitation, analysis of options, yielding figures for the assessment of the economic implications of the bridge rehabilitation work and the environmental impacts of the bridge rehabilitation options and of the associated secondary effects respectively. The overall monitoring system will be evaluated and benchmarked on actual bridges of Egnatia Highway (Greece) and Bosporus Bridge (Turkey).
Y1  - 2019
SN  - 978-1-315-22891-4
SN  - 978-1-138-62633-1
SP  - 2085
EP  - 2092
PB  - CRC Press, Taylor & Francis Group
CY  - Boca Raton
ER  - 
TY  - JOUR
A1  - Qiu, Xunlin
A1  - Groth, Frederick
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Cellular polypropylene foam films as DC voltage insulation and as piezoelectrets
BT  - a comparison
JF  - IEEE transactions on dielectrics and electrical insulation
N2  - Polymer foams are in industrial use for several decades. More recently, non-polar polymer foams were found to be piezoelectric (so-called piezoelectrets) after internal electrical charging of the cavities. So far, few studies have been carried out on the electrical-insulation properties of polymer foams. Here, we compare the piezoelectric and the DC-voltage electrical-insulation properties of cellular polypropylene (PP) foams. Their cavity microstructure can be adjusted via inflation in high-pressure nitrogen gas in combination with a subsequent thermal treatment. While inflation is effective for improving the piezoelectricity, it is detrimental for the electrical-insulation properties. The original cellular PP foam shows a breakdown strength of approximately 230 MV/m, within the same range as that of solid PP. The breakdown strength decreases with increasing degree of inflation, and the dependence on the foam thickness follows an inverse power law with an exponent of 1.2. Nevertheless, up to a thickness of 140 mu m (3.5 times the original thickness), the breakdown strength of cellular-foam PP films is at least 7 times that of an air gap with the same thickness. In addition, the influence of high temperatures and high humidities on the piezoelectricity and the breakdown strength of cellular PP was studied. It was found that the piezoelectric d(33) coefficient decays rapidly already at 70 degrees C, while the breakdown strength slightly increases during storage at 70 or 90 degrees C. Under a relative humidity of 95%, the breakdown strength increases with storage time, while the piezoelectric d(33) coefficient slightly decreases.
KW  - Cellular polypropylene (PP)
KW  - polymer-foam films
KW  - ferro- and piezoelectrets
KW  - charge storage
KW  - electrical breakdown
KW  - dielectric barrier discharges
Y1  - 2018
U6  - https://doi.org/10.1109/TDEI.2018.007192
SN  - 1070-9878
SN  - 1558-4135
VL  - 25
IS  - 3
SP  - 829
EP  - 834
PB  - Institut of Electr. and Electronics Engineers
CY  - Piscataway
ER  - 
TY  - GEN
A1  - Loupos, Konstantinos
A1  - Damigos, Yannis
A1  - Amditis, Angelos
A1  - Gerhard, Reimund
A1  - Rychkov, Dmitry
A1  - Wirges, Werner
A1  - Schulze, Manuel
A1  - Lenas, Sotiris-Angelos
A1  - Chatziandreoglou, Christos
A1  - Malliou, Christina
A1  - Tsaoussidis, Vassilis
A1  - Brady, Ken
A1  - Frankenstein, Bernd
T1  - Structural health monitoring system for bridges based on skin-like sensor
T2  - IOP conference series : Materials science and engineering
N2  - Structural health monitoring activities are of primal importance for managing transport infrastructure, however most SHM methodologies are based on point-based sensors that have limitations in terms of their spatial positioning requirements, cost of development and measurement range. This paper describes the progress on the SENSKIN EC project whose objective is to develop a dielectric-elastomer and micro-electronics-based sensor, formed from a large highly extensible capacitance sensing membrane supported by advanced microelectronic circuitry, for monitoring transport infrastructure bridges. Such a sensor could provide spatial measurements of strain in excess of 10%. The actual sensor along with the data acquisition module, the communication module and power electronics are all integrated into a compact unit, the SENSKIN device, which is energy-efficient, requires simple signal processing and it is easy to install over various surface types. In terms of communication, SENSKIN devices interact with each other to form the SENSKIN system; a fully distributed and autonomous wireless sensor network that is able to self-monitor. SENSKIN system utilizes Delay-/Disruption-Tolerant Networking technologies to ensure that the strain measurements will be received by the base station even under extreme conditions where normal communications are disrupted. This paper describes the architecture of the SENSKIN system and the development and testing of the first SENSKIN prototype sensor, the data acquisition system, and the communication system.
Y1  - 2017
U6  - https://doi.org/10.1088/1757-899X/236/1/012100
SN  - 1757-8981
VL  - 236
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Qiu, Xunlin
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Thermal poling of ferroelectrets: How does the gas temperature influence dielectric barrier discharges in cavities?
JF  - Applied physics letters
N2  - The influence of the temperature in the gas-filled cavities on the charging process of ferroelectret film systems has been studied in hysteresis measurements. The threshold voltage and the effective polarization of the ferroelectrets were determined as functions of the charging temperature TP. With increasing TP, the threshold voltage for triggering dielectric barrier discharges in ferroelectrets decreases. Thus, increasing the temperature facilitates the charging of ferroelectrets. However, a lower threshold voltage reduces the attainable remanent polarization because back discharges occur at lower charge levels, as soon as the charging voltage is turned off. The results are discussed in view of Paschen's law for electrical breakdown, taking into account the respective gas temperature and a simplified model for ferroelectrets. Our results indicate that the thermal poling scheme widely used for conventional ferroelectrics is also useful for electrically charging ferroelectrets.
Ferroelectrets (sometimes also called piezoelectrets) are relatively new members of the family of piezo-, pyro-, and ferroelectric materials.1–5 As their name indicates, ferroelectrets are space-charge electrets that show ferroic behavior. They are non-uniform electret materials or materials systems with electrically charged internal cavities. As space-charge electrets, ferroelectrets usually do not contain any molecular dipoles. However, the cavities inside the material can be turned into macroscopic dipoles through a series of micro-plasma discharges at high electric fields, so-called dielectric barrier discharges (DBDs).6–8 The gas inside the cavities is ionized when the internal electric field exceeds the threshold for electrical breakdown, generating charges of both polarities.9 The positive and negative charges travel in opposite directions, and are eventually trapped at the internal top and bottom surfaces of the cavities, respectively. After charging, the cavities may be regarded as macroscopic dipoles that can be switched by reversing the applied voltage.
An electric-polarization-vs.-electric-field (P(E)) hysteresis is considered as an essential criterion for ferroelectricity. P(E)-hysteresis curves are usually characterized by the spontaneous polarization, the coercive field, and the remanent polarization. Recently, we have demonstrated P(E)-hysteresis loops on two different types of ferroelectrets, namely, cellular polypropylene ferroelectrets and tubular-channel fluoroethylene-polypropylene copolymer ferroelectrets.10,11 The P(E)-hysteresis loops not only prove the ferroic behavior of ferroelectrets, but also allow us to determine such parameters as the coercive field and the remanent polarization.
It is widely accepted that Paschen breakdown is the underlying mechanism for the inception of DBDs in ferroelectrets.12–14 On this basis, the charging behavior and the resulting piezoelectricity of ferroelectrets in different gases at various pressures have been studied.15–17 Paschen's law describes the conditions for electrical breakdown in a gas at a constant temperature (usually room temperature), and it needs to be modified for gas breakdown at other temperatures. The temperature stability of the piezoelectricity in ferroelectrets after charging at elevated temperatures was investigated by several researchers.18–21 Recently, a preliminary report about the effects of the charging temperature on the hysteresis loops in ferroelectrets has been presented.22
In this letter, the influence of the gas temperature on the charging of ferroelectret systems is investigated in more detail by means of quasi-ferroelectric hysteresis-loop measurements. Teflon™ fluoroethylenepropylene (FEP) copolymer samples with tubular channels were prepared via thermal lamination as described previously.23 To this end, two FEP films with a thickness of 50 μm each were laminated at 300 ° C
around a 100 μm thick polytetrafluoroethylene (PTFE) template (total area 35 mm × 45 mm) that contains parallel rectangular openings (area 1.5 mm × 40 mm each). After lamination, the template was removed, which results in an FEP film system with open tubular channels. The samples were metallized on both surfaces with aluminum electrodes of 20 mm diameter.
P(E)-hysteresis loops were obtained with a modified Sawyer–Tower (ST) circuit.10,11 A high-voltage (HV) capacitor C1 (3 nF) and a large standard capacitor Cm (1 μF) were connected in series with the sample. A bipolar sinusoidal voltage with a frequency of 10 mHz was applied from an HV power supply (FUG HCB 7-6500) controlled by an arbitrary-waveform generator (HP 33120a). The voltage Vout
on Cm is measured by means of an electrometer (HP 3458a), and the charge flowing through the circuit is determined as Q(t)=CmVout(t)
. The experiments were carried out at isothermal conditions in a Novocontrol® Quatro cryosystem.
With the modified ST circuit, Q–V loops have been measured on a tubular-channel FEP ferroelectret system at different temperatures. The sample capacitance of about 34.5 pF is determined by a linear fit of the initial part of the Q–V curve recorded at 20 °C
, where the voltage has been raised up from zero on a fresh sample. The hysteresis loops are obtained from the Q–V curves by subtracting the contribution that results from charging of the sample capacitance.10 Figure 1 shows the hysteresis loops of the sample at −100, 0, and +100 ° C, respectively. According to previous theoretical and experimental studies,24,25 the length of each of the horizontal sides of the parallelogram-like hysteresis loops is given by 2Vth where Vth is the threshold voltage. As the charging temperature decreases, the hysteresis loop becomes wider and less high, i.e., the threshold voltage increases, while the polarization at maximum voltage decreases.
Y1  - 2016
U6  - https://doi.org/10.1063/1.4954263
SN  - 0003-6951
SN  - 1077-3118
VL  - 108
SP  - 1687
EP  - 1697
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Mazurek, P.
A1  - Yu, L.
A1  - Gerhard, Reimund
A1  - Wirges, Werner
A1  - Skov, A. L.
T1  - Glycerol as high-permittivity liquid filler in dielectric silicone elastomers
JF  - Journal of applied polymer science
N2  - A recently reported novel class of elastomers was tested with respect to its dielectric properties. The new elastomer material is based on a commercially available poly(dimethylsiloxane) composition, which has been modified by embedding glycerol droplets into its matrix. The approach has two major advantages that make the material useful in a dielectric actuator. First, the glycerol droplets efficiently enhance the dielectric constant, which can reach astonishingly high values in the composite. Second, the liquid filler also acts as a softener that effectively decreases the elastic modulus of the composite. In combination with very low cost and easy preparation, the two property enhancements lead to an extremely attractive dielectric elastomer material. Experimental permittivity data are compared to various theoretical models that predict relative permittivity changes as a function of filler loading, and the applicability of the models is discussed. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44153.
KW  - crosslinking
KW  - dielectric properties
KW  - elastomers
KW  - sensors and actuators
Y1  - 2016
U6  - https://doi.org/10.1002/app.44153
SN  - 0021-8995
SN  - 1097-4628
VL  - 133
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Holländer, Lars
A1  - Kossack, Wilhelm
A1  - Kollosche, Matthias
A1  - Wirges, Werner
A1  - Kremer, Friedrich
A1  - Gerhard, Reimund
T1  - Influence of the remanent polarisation on the liquid crystal alignment in composite films of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and a cyanobiphenyl-based liquid crystal
JF  - Liquid crystals : an international journal of science and technology
N2  - Polymer-dispersed liquid crystals (PDLCs) of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and nematic 4-cyano-4ʹ-n-hexylbiphenyl (6CB) or 4-cyano-4ʹ-n-pentylbiphenyl (5CB) were prepared to study the effect of the remanent polarisation of the polymer on the liquid crystal alignment. We measured the macroscopic alignment of the liquid crystal molecules in the thickness direction by means of Infrared Transition-Moment Orientational Analysis. Electrical poling at 100 V/µm caused an increased order parameter up to 0.15. After subsequent annealing above the nematic-to-isotropic phase-transition temperature, the order parameter was reduced to 0.02. Nevertheless, the order parameter was still higher than for non-poled film indicating a slight orientation in thickness direction. Both values are lower than those expected from model calculations. In agreement with dielectric measurements, we attribute this result to the shielding effect of mobile charge carriers within the liquid crystal inclusions.
KW  - Polymer-dispersed liquid crystal
KW  - ferroelectric polymer
KW  - remanent polarisation
KW  - liquid crystal alignment
Y1  - 2016
U6  - https://doi.org/10.1080/02678292.2016.1185174
SN  - 0267-8292
SN  - 1366-5855
VL  - 43
SP  - 1514
EP  - 1521
PB  - Editions Rodopi BV
CY  - Abingdon
ER  - 
TY  - JOUR
A1  - Sborikas, Martynas
A1  - Qiu, Xunlin
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Jenninger, Werner
A1  - Lovera, Deliani
T1  - Screen printing for producing ferroelectret systems with polymer-electret films and well-defined cavities
JF  - Applied physics : A, Materials science & processing
N2  - We report a process for preparing polymer ferroelectrets by means of screen printing-a technology that is widely used for the two-dimensional patterning of printed layers. In order to produce polymer-film systems with cavities that are suitable for bipolar electric charging, a screen-printing paste is deposited through a screen with a pre-designed pattern onto the surface of a polymer electret film. Another such polymer film is placed on top of the printed pattern, and well-defined cavities are formed in-between. During heating and curing, the polymer films are tightly bonded to the patterned paste layer so that a stable three-layer system is obtained. In the present work, polycarbonate (PC) films have been employed as electret layers. Screen printing, curing and charging led to PC ferroelectret systems with a piezoelectric d (33) coefficient of about 28 pC/N that is stable up to 100 C-a similar to. Due to the rather soft patterned layer, d (33) strongly decreases already for static pressures of tens of kPa. The results demonstrate the suitability of screen printing for the preparation of ferroelectret systems.
Y1  - 2014
U6  - https://doi.org/10.1007/s00339-013-7998-3
SN  - 0947-8396
SN  - 1432-0630
VL  - 114
IS  - 2
SP  - 515
EP  - 520
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Qiu, Xunlin
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Polarization and Hysteresis in Tubular-Channel Fluoroethylenepropylene-Copolymer Ferroelectrets
JF  - Ferroelectrics
N2  - Polarization-vs.-applied-voltage hysteresis curves are recorded on tubular-channel fluoroethylene-propylene (FEP) copolymer ferroelectrets by means of a modified Sawyer-Tower circuit. Dielectric barrier discharges (DBDs) inside the cavities are triggered when the applied voltage is sufficiently high. During the DBDs, the cavities become man-made macroscopic dipoles which build up an effective polarization in the ferroelectret. Therefore, a phenomenological hysteresis curve is observed. From the hysteresis loop, the remanent polarization and the coercive field can be determined. Furthermore, the polarization can be related to the respective piezoelectric coefficient of the ferroelectret. The proposed method is easy to implement and is useful for characterization, further development and optimization of ferro- or piezoelectrets.
KW  - Ferroelectrets
KW  - piezoelectrets
KW  - tubular-channel polymer systems
KW  - dielectric barrier discharge (DBD)
KW  - fluoroethylenepropylene (FEP) copolymer
KW  - piezoelectricity-polarization relation
Y1  - 2014
U6  - https://doi.org/10.1080/00150193.2014.964603
SN  - 0015-0193
SN  - 1563-5112
VL  - 472
IS  - 1
SP  - 100
EP  - 109
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  - 
TY  - JOUR
A1  - Qiu, Xunlin
A1  - Holländer, Lars
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Basso, Heitor Cury
T1  - Direct hysteresis measurements on ferroelectret films by means of a modified Sawyer-Tower circuit
JF  - Journal of applied physics
N2  - Ferro- and piezo-electrets are non-polar polymer foams or film systems with internally charged cavities. Since their invention more than two decades ago, ferroelectrets have become a welcome addition to the range of piezo-, pyro-, and ferro-electric materials available for device applications. A polarization-versus-electric-field hysteresis is an essential feature of a ferroelectric material and may also be used for determining some of its main properties. Here, a modified Sawyer-Tower circuit and a combination of unipolar and bipolar voltage waveforms are employed to record hysteresis curves on cellular-foam polypropylene ferroelectret films and on tubular-channel fluoroethylenepropylene copolymer ferroelectret film systems. Internal dielectric barrier discharges (DBDs) are required for depositing the internal charges in ferroelectrets. The true amount of charge transferred during the internal DBDs is obtained from voltage measurements on a standard capacitor connected in series with the sample, but with a much larger capacitance than the sample. Another standard capacitor with a much smaller capacitance-which is, however, still considerably larger than the sample capacitance-is also connected in series as a high-voltage divider protecting the electrometer against destructive breakdown. It is shown how the DBDs inside the polymer cavities lead to phenomenological hysteresis curves that cannot be distinguished from the hysteresis loops found on other ferroic materials. The physical mechanisms behind the hysteresis behavior are described and discussed.
Y1  - 2013
U6  - https://doi.org/10.1063/1.4809556
SN  - 0021-8979
VL  - 113
IS  - 22
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Basso, Heitor Cury
A1  - Qiu, Xunlin
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Temporal evolution of the re-breakdown voltage in small gaps from nanoseconds to milliseconds
JF  - Applied physics letters
N2  - A detailed understanding of electric breakdown in dielectrics is of scientific and technological interest. In gaseous dielectrics, a so-called re-breakdown is sometimes observed after extinction of the previous discharge. Although time-dependent re-breakdown voltage is essentially known, its behavior immediately after the previous discharge is not precisely understood. We present an electronic circuit for accurate measurements of the time-dependent re-breakdown voltage in small gaps from tens of nanoseconds to several milliseconds after the previous spark. Results from such experiments are compared with earlier findings, and relevant physical mechanisms such as heating of the gas, decay of the plasma, and ionization of excited atoms and molecules are discussed. It is confirmed that the thermal model is not valid at times below several microseconds.
Y1  - 2013
U6  - https://doi.org/10.1063/1.4773518
SN  - 0003-6951
VL  - 102
IS  - 1
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Wirges, Werner
A1  - Raabe, Sebastian
A1  - Qiu, Xunlin
T1  - Dielectric elastomer and ferroelectret films combined in a single device how do they reinforce each other?
JF  - Applied physics : A, Materials science & processing
N2  - Dielectric elastomers (DE) are soft polymer materials exhibiting large deformations under electrostatic stress. When a prestretched elastomer is stuck to a flat plastic frame, a complex structure that can be used as an actuator (DEA) is formed due to self-organization and energy minimization. Here, such a DEA was equipped with a ferroelectret film. Ferroelectrets are internally charged polymer foams or void-containing polymer-film systems combining large piezoelectricity with mechanical flexibility and elastic compliance. In their dielectric spectra, ferroelectrets show piezoelectric resonances that can be used to analyze their electromechanical properties. The antiresonance frequencies ( ) of ferroelectret films not only are directly related to their geometric parameters, but also are sensitive to the boundary conditions during measurement. In this paper, a fluoroethylenepropylene (FEP) ferroelectret film with tubular void channels was glued to a plastic frame prior to the formation of self-organized minimum-energy DEA structure. The dielectric resonance spectrum (DRS) of the ferroelectret film was measured in-situ during the actuation of the DEA under applied voltage. It is found that the antiresonance frequency is a monotropic function of the bending angle of the actuator. Therefore, the actuation of DEAs can be used to modulate the of ferroelectrets, while the can also be taken for in-situ diagnosis and for precise control of the actuation of the DEA. Combination of DEAs and ferroelectrets brings a number of possibilities for application.
Y1  - 2012
U6  - https://doi.org/10.1007/s00339-012-6833-6
SN  - 0947-8396
SN  - 1432-0630
VL  - 107
IS  - 3
SP  - 583
EP  - 588
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Wertheimer, Michael R.
A1  - St-Georges-Robillard, Amelie
A1  - Lerouge, Sophie
A1  - Mwale, Fackson
A1  - Elkin, Bentsian
A1  - Oehr, Christian
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Amine-rich organic thin films for cell culture - possible electrostatic effects in cell-surface interactions
JF  - Japanese journal of applied physics
N2  - In recent communications from these laboratories, we observed that amine-rich thin organic layers are very efficient surfaces for the adhesion of mammalian cells. We prepare such deposits by plasma polymerization at low pressure, atmospheric pressure, or by vacuum-ultraviolet photo-polymerization. More recently, we have also investigated a commercially available material, Parylene diX AM. In this article we first briefly introduce literature relating to electrostatic interactions between cells, proteins, and charged surfaces. We then present certain selected cell-response results that pertain to applications in orthopedic and cardiovascular medicine: we discuss the influence of surface properties on the observed behaviors of two particular cell lines, human U937 monocytes, and Chinese hamster ovary cells. Particular emphasis is placed on possible electrostatic attractive forces due to positively charged R-NH3+ groups and negatively charged proteins and cells, respectively. Experiments carried out with electrets, polymers with high positive or negative surface potentials are added for comparison.
Y1  - 2012
U6  - https://doi.org/10.1143/JJAP.51.11PJ04
SN  - 0021-4922
VL  - 51
IS  - 11
PB  - Japan Soc. of Applied Physics
CY  - Tokyo
ER  - 
TY  - JOUR
A1  - Altafim, Ruy Alberto Pisani
A1  - Rychkov, Dmitry
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Basso, Heitor Cury
A1  - Altafim, Ruy Alberto Pisani
A1  - Melzer, Martin
T1  - Laminated tubular-channel ferroelectret systems from low-density Polyethylene Films and from Fluoroethylene-propylene Copolymer Films - A comparison
JF  - IEEE transactions on dielectrics and electrical insulation
N2  - A template-based lamination technique for the manufacture of ferroelectrets from uniform electret films was recently reported. In the present work, this technique is used to prepare similar ferroelectret structures from low-density polyethylene (LDPE) films and from fluoro-ethylene-propylene (FEP) copolymer films. A comparative analysis of the pressure-, temperature-, and frequency-dependent piezoelectric properties has been performed on the two ferroelectret systems. It is observed that the FEP ferroelectrets exhibit better piezoelectric responses and are thermally more stable. The difference between the piezoelectric d(33) coefficients of the two ferroelectret systems is partially explained here by their different elastic moduli. The anti-resonance peaks of both structures have been investigated by means of dielectric resonance spectroscopy and electroacoustic sound-pressure measurements. A difference of more than 10 kHz is observed between the anti-resonance frequencies of the two ferroelectret systems.
KW  - Ferroelectrets
KW  - piezoelectrets
KW  - piezoelectricity
KW  - electro-mechanical transducers
KW  - static-pressure dependence
KW  - temperature dependence
KW  - frequency response
Y1  - 2012
SN  - 1070-9878
VL  - 19
IS  - 4
SP  - 1116
EP  - 1123
PB  - Inst. of Electr. and Electronics Engineers
CY  - Piscataway
ER  - 
TY  - JOUR
A1  - Altafim, Ruy Alberto Pisani
A1  - Altafim, Ruy Alberto Pisani
A1  - Qiu, Xunlin
A1  - Raabe, Sebastian
A1  - Wirges, Werner
A1  - Basso, Heitor Cury
A1  - Gerhard, Reimund
T1  - Fluoropolymer piezoelectrets with tubular channels resonance behavior controlled by channel geometry
JF  - Applied physics : A, Materials science & processing
N2  - Ferro- or piezoelectrets are dielectric materials with two elastically very different macroscopic phases and electrically charged interfaces between them. One of the newer piezoelectret variants is a system of two fluoroethylenepropylene (FEP) films that are first laminated around a polytetrafluoroethylene (PTFE) template. Then, by removing the PTFE template, a two-layer FEP structure with open tubular channels is obtained. After electrical charging, the channels form easily deformable macroscopic electric dipoles whose changes under mechanical or electrical stress lead to significant direct or inverse piezoelectricity, respectively. Here, different PTFE templates are employed to generate channel geometries that vary in height or width. It is shown that the control of the channel geometry allows a direct adjustment of the resonance frequencies in the tubular-channel piezoelectrets. By combining several different channel widths in a single ferroelectret, it is possible to obtain multiple resonance peaks that may lead to a rather flat frequency-response region of the transducer material. A phenomenological relation between the resonance frequency and the geometrical parameters of a tubular channel is also presented. This relation may help to design piezoelectrets with a specific frequency response.
Y1  - 2012
U6  - https://doi.org/10.1007/s00339-012-6848-z
SN  - 0947-8396
VL  - 107
IS  - 4
SP  - 965
EP  - 970
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Fang, Peng
A1  - Hollaender, Lars
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Piezoelectric d(33) coefficients in foamed and layered polymer piezoelectrets from dynamic mechano-electrical experiments, electro-mechanical resonance spectroscopy and acoustic-transducer measurements
JF  - Measurement science and technology
N2  - Piezoelectrets are novel transducer materials which can be widely applied in sensors and actuators. Here, three techniques for determining piezoelectric d(33) coefficients of piezoelectrets are reviewed and compared. Two types of piezoelectrets, polyethylene-naphthalate (PEN) polymer-foam piezoelectrets and fluorinated ethylene-propylene (FEP) copolymer-layer piezoelectrets, have been prepared and measured by means of dynamic, resonance, and acoustical methods. The dynamic measurements show that the d(33) coefficient of PEN-foam samples clearly decreases with increasing stress, but 80% of the initial d(33) can be retained after 1800 cycles of a continuous dynamic measurement in a mechanical fatigue test. The resonance measurements demonstrate that both PEN-foam and FEP-layer samples exhibit clear electro-mechanical resonances. PEN-foam samples show elastic moduli in the range from 1 to 12 MPa and d(33) values up to 500 pC N-1, while FEP-layer samples show homogeneous elastic moduli of about 0.3 MPa and d(33) values of about 280 pC N-1. The acoustical measurements reveal that both PEN-foam and FEP-layer samples exhibit stable frequency responses in the range from 5.7 to 20 kHz. In addition, d(33) coefficients obtained with different experimental methods are in good agreement with each other, which confirms the reliability of all three techniques.
KW  - piezoelectret
KW  - ferroelectret
KW  - dielectric resonance spectroscopy
KW  - piezoelectric measurements
KW  - acoustic-transducer materials
KW  - polyethylene naphthalate (PEN)
KW  - fluorinated ethylene-propylene copolymer (FEP)
Y1  - 2012
U6  - https://doi.org/10.1088/0957-0233/23/3/035604
SN  - 0957-0233
VL  - 23
IS  - 3
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Fang, Peng
A1  - Wang, Feipeng
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Basso, Heitor Cury
T1  - Three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films
JF  - Applied physics : A, Materials science & processing
N2  - A process for preparing three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films is introduced. Samples are made from commercial FEP films by means of laser cutting, laser bonding, electrode evaporation, and high-field poling. The observed dielectric-resonance spectra demonstrate the piezoelectricity of the FEP sandwiches. Piezoelectric d (33) coefficients up to a few hundred pC/N are achieved. Charging at elevated temperatures can increase the thermal stability of the piezoelectrets. Isothermal experiments for approximately 15 min demonstrate that samples charged at 140A degrees C keep their piezoelectric activity up to at least 120A degrees C and retain 70% of their initial d (33) even at 130A degrees C. Acoustical measurements show a relatively flat frequency response in the range between 300 Hz and 20 kHz.
Y1  - 2011
U6  - https://doi.org/10.1007/s00339-010-6008-2
SN  - 0947-8396
SN  - 1432-0630
VL  - 103
IS  - 2
SP  - 455
EP  - 461
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Sun, Zhuanlan
A1  - Zhang, Xiaoqing
A1  - Xia, Zhongfu
A1  - Qiu, Xunlin
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Zeng, Changchun
A1  - Zhang, Chuck
A1  - Wang, Ben
T1  - Polarization and piezoelectricity in polymer films with artificial void structure
JF  - Applied physics : A, Materials science & processing
N2  - Laminated polymer-film systems with well-defined void structures were prepared from fluoroethylenepropylene (FEP) and polytetrafluoroethylene (PTFE) layers. First the PTFE films were patterned and then fusion-bonded with the FEP films. The laminates were subjected to either corona or contact charging in order to obtain the desired piezoelectricity. The build-up of the "macro-dipoles" in the laminated films was studied by recording the electric hysteresis loops. The resulting electro-mechanical properties were investigated by means of dielectric resonance spectroscopy (DRS) and direct measurements of the stress-strain relationship. Moreover, the thermal stability of the piezoelectric d (33) coefficient was investigated at elevated temperatures and via thermally stimulated discharge (TSD) current measurements in short circuit. For 150 mu m thick laminated films, consisting of one 25 mu m thick PTFE layer, two 12.5 mu m thick FEP layers, and a void of 100 mu m height, the critical voltage necessary for the build-up of the "macro-dipoles" in the inner voids was approximately 1400 V, which agrees with the value calculated from the Paschen Law. A quasi-static piezoelectric d (33) coefficient up to 300 pC/N was observed after corona charging. The mechanical properties of the film systems are highly anisotropic. At room temperature, the Young's moduli of the laminated film system are around 0.37 MPa in the thickness direction and 274 MPa in the lateral direction, respectively. Using these values, the theoretical shape anisotropy ratio of the void was calculated, which agrees well with experimental observation. Compared with films that do not exhibit structural regularity, the laminates showed improved thermal stability of the d (33) coefficients. The thermal stability of d (33) can be further improved by pre-aging. E.g., the reduction of the d (33) value in the sample pre-aged at 150A degrees C for 5 h was less than 5% after annealing for 30 h at a temperature of 90A degrees C.
Y1  - 2011
U6  - https://doi.org/10.1007/s00339-011-6481-2
SN  - 0947-8396
VL  - 105
IS  - 1
SP  - 197
EP  - 205
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Qiu, Xunlin
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Beneficial and detrimental fatigue effects of dielectric barrier discharges on the piezoelectricity of polypropylene ferroelectrets
JF  - Journal of applied physics
N2  - Cellular polypropylene (PP) ferroelectrets combine a large piezoelectricity with mechanical flexibility and elastic compliance. Their charging process represents a series of dielectric barrier discharges (DBDs) that generate a cold plasma with numerous active species and thus modify the inner polymer surfaces of the foam cells. Both the threshold for the onset of DBDs and the piezoelectricity of ferroelectrets are sensitive to repeated DBDs in the voids. It is found that the threshold voltage is approximately halved and the charging efficiency is clearly improved after only 10(3) DBD cycles. However, plasma modification of the inner surfaces from repeated DBDs deteriorates the chargeability of the voids, leading to a significant reduction of the piezoelectricity in ferroelectrets. After a significant waiting period, the chargeability of previously fatigued voids shows a partial recovery. The plasma modification is, however, detrimental to the stability of the deposited charges and thus also of the macroscopic dipoles and of the piezoelectricity. Fatigue from only 10(3) DBD cycles already results in significantly less stable piezoelectricity in cellular PP ferroelectrets. The fatigue rate as a function of the number of voltage cycles follows a stretched exponential. Fatigue from repeated DBDs can be avoided if most of the gas molecules inside the voids are removed via a suitable evacuation process.
Y1  - 2011
U6  - https://doi.org/10.1063/1.3610507
SN  - 0021-8979
SN  - 1089-7550
VL  - 110
IS  - 2
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Wang, Feipeng
A1  - Frübing, Peter
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Wegener, Michael
T1  - Enhanced Polarization in Melt-quenched and Stretched Poly(vinylidene Fluoride-Hexafluoropropylene) Films
N2  - beta-phase poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer films were prepared by uniaxially stretching solution-cast or melt-quenched samples. Different preparation routes lead to different amounts of the crystalline alpha and beta phases in the films, as detected by means of Fourier-transform infrared spectroscopy and X-ray diffractometry. The beta phase is significantly enhanced in melt-quenched and stretched films in comparison to solution-cast and stretched films. This is particularly true for copolymer samples with higher HFP content. The beta- phase enhancement is also observed in ferroelectric-hysteresis experiments where a rather high polarization of 58 mC/ m(2) was found on melt-quenched and stretched samples after poling at electric fields of 140 MV/m. After poling at 160 MV/m, one of these samples exhibited a piezoelectric d(33) coefficient as high as 21 pC/N. An electric-field-induced partial transition from the alpha to the beta phase was also observed on the melt-quenched and stretched samples. This effect leads to a further increase in the applications-relevant dipole polarization. Uniaxially stretched ferroelectric- polymer films are highly anisotropic. Dielectric resonance spectroscopy reveals a strong increase of the transverse piezoelectric d(32) coefficient and a strong decrease of the transverse elastic modulus c(32) upon heating from 20 to 50 degrees C.
Y1  - 2010
UR  - http://ieeexplore.ieee.org/servlet/opac?punumber=94
U6  - https://doi.org/10.1109/TDEI.2010.5539679
SN  - 1070-9878
ER  -